I'm about a half hour west of Chicago, and I was outside smoking when I saw this thread. I admit, the second I read the title I looked straight up...
As if the "UFO" would be there with impeccable timing.

Sadly it wasn't, but thanks for posting. I'll report here if I should see/hear anything skywise.

It seems that Green Fireballs have their own Wikipedia page! Interesting. It says that
UFOlogists consider the green balls as some of the best documented examples of UFO's, if that counts for anything.

Green balls/lights sightings have been posted here recently too. The Aircraft Projects forum people that are "In the know" say it is used on black
project/experimental aircrafts. I think it is most likely what they saw was this experimental aircraft and not an alien UFO.

I am not certain, but as I said a couple posts up it could be black project/Experimental aircraft. A green light is being used on the fuselage of
certain testing craft currently. There have been many sightings of similar green lights. Check out this thread:

Could it have been a bolide/fireball meteor (which is one possibility you also suspected).

"Green fireballs leaving a trail" could be a description of a bolide.

EDIT TO ADD:

Here is an EXAMPLE of a green bolide meteorite. This is NOT the one in the OP, but rather is the "Peekskill Meteorite" of 1992, so named because a
piece of it ended up hitting the ground in Peekskill, New York (after hitting a parked car first).

I could see how people may describe this as a "green fireball UFO". By the way, I witnessed this "Peekskill Meteorite" fireball myself in
Pennsylvania back in 1992.

edit on 7/14/2014 by Soylent Green Is People because: (no reason given)

But I have a questions for anyone who was in Chicago on 9/11. Am I the only one who remembers seeing blue lights/balls in the sky? I remember
talking to my mother and we both thought it had to be some type of satellite or military shield (since there was no air traffic). But I never heard
anyone mention these?

I've seen this is Las Vegas 2 times in about 4 years and it really made me wonder what the heck it was. Green fireball flying low and not fast enough
to be a meteor but too bright to be a plane and it just disappeared each time within a few seconds. The last time I saw it it was passing horizontally
in front of a helicopter near the Encore casino about a year ago.

I've seen this is Las Vegas 2 times in about 4 years and it really made me wonder what the heck it was. Green fireball flying low and not fast enough
to be a meteor but too bright to be a plane and it just disappeared each time within a few seconds. The last time I saw it it was passing horizontally
in front of a helicopter near the Encore casino about a year ago.

Its apparent speed would depend on its angle of approach to you. If it was coming straight at you you might not see much motion at all but travelling
perpendicular it would appear quite fast.

I've seen this is Las Vegas 2 times in about 4 years and it really made me wonder what the heck it was. Green fireball flying low and not fast enough
to be a meteor but too bright to be a plane and it just disappeared each time within a few seconds. The last time I saw it it was passing horizontally
in front of a helicopter near the Encore casino about a year ago.

Its apparent speed would depend on its angle of approach to you. If it was coming straight at you you might not see much motion at all but travelling
perpendicular it would appear quite fast.

If it was a meteor, it would also depend on at what point of its trip throug hthe atmosphere it is.

A bolide fireball meteor may be moving very fast at first, but as it travels through the thick atmosphere, it slows down. a meteor such as the
one I showed in the video above (the "Peekskill Meteor") may have slow down to only a few thousand mph by the time it started breaking up. By the
time the small-ish broken up pieces of meteorite hit the ground, they are only moving at terminal velocity (maybe 200 mph) -- although, granted, by
that time they are no longer glowing fireballs.

Here's another video of that same 1992 "Peekskill Meteor" as it flies over Pittsburgh, Pennsylvania. You can see that it does not appear to be
moving that fast relative to the buildings (although it is still moving at a few thousand mph, but high enough that it looks slow):

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